Air Percussion Drilling In Horizontal Wells

ABSTRACT

A method of drilling a subterranean formation includes positioning a drill string in a well bore in the subterranean formation. The drill string includes a hammer bit, a bend in a housing of the drill string, and a guidance system that determines inclination and azimuth of at least a portion of the drill string in the well bore. Once positioned in the well bore, the hammer bit is caused to repeatedly strike the end of the well bore while rotating about an axis of the hammer bit thereby drilling the subterranean formation and forming a new length of the well bore in the subterranean formation. The orientation of the bend of the drill string in the well bore is controlled based on the determined inclination and azimuth such that the hammer bit drills the new length of the well bore substantially horizontally in the subterranean formation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application Nos. 61/302,331, filed Feb. 8, 2010, entitled “Air Percussion Drilling in Horizontal Wells”, and 61/297,447, filed Jan. 22, 2010, also entitled “Air Percussion Drilling in Horizontal Wells”, both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of accessing one or more resources from a subterranean foil nation.

2. Description of Related Art

Subterranean deposits or formations of coal contain substantial quantities of entrained methane gas. Heretofore, the drilling of horizontal or substantially horizontal wells in such subterranean formations was accomplished utilizing either a polycrystalline diamond compact (PDC) bit or a tri-cone drill bit. It has been observed that abrasive formations destroy PDC bits very quickly and can wear away tri-cone bits so quickly that one horizontal well requires several different tri-cone bits and may be uneconomical.

Heretofore, the combination of an air hammer and a hammer bit have proven to be effective for drilling certain sections of a well bore in hard rock. This combination uses high-frequency impacts to overcome the compressive strength of a rock formation and has achieved high rates of penetration. Applications of the combination of an air hammer and a hammer bit have been in straight vertical wells in high compressive strength formations that have little or no water or oil content. Several high angle well bores, up to 80% inclination, utilizing packed-hole directional assemblies and single shot guidance have also been drilled utilizing the combination of an air hammer and a hammer bit.

With single shot guidance, a drill string is utilized to initially form a well bore. At a suitable time when it is desired to determine the direction of the well bore, the drill string is removed from the well bore and a guidance system that includes suitable means known in the art for determining inclination and azimuth is lowered into the well bore. Once it is in place in the well bore, the guidance system transmits azimuth and inclination data and/or signals from its location in the well bore to the surface where said azimuth and inclination data and/or signals is/are interpreted and the direction of the well bore is determined therefrom. Thereafter, the guidance system is removed from the well bore. If further drilling of the well bore is desired, the drill string is returned into the well bore for this purpose. If required and/or desired, a new drill bit can be installed on the drill string prior to returning it into the well bore.

SUMMARY OF THE INVENTION

Disclosed herein is a method of drilling a subterranean foil nation. The method includes: (a) forming a well bore from a surface into the subterranean formation; (b) positioning a bottom hole assembly at an end of the well bore in the subterranean formation, the bottom hole assembly including in order between the end of the well bore and the surface: a hammer bit; a percussion hammer operative for causing the hammer bit to move alternately into and out of contact with the end of the well bore; a motor assembly having a first end coupled to the percussion hammer, the motor assembly including a motor operative for rotating the percussion hammer and the hammer bit about central axes of the percussion hammer and the hammer bit, the motor assembly including a motor housing having a bend therein that defines an angle between the first end of the motor assembly, which is desirably aligned with the percussion hammer and the hammer bit, and a second end of the motor assembly; and a guidance system operative for determining inclination and azimuth of at least a portion of the bottom hole assembly in the well bore and for generating one or more signals regarding the inclination and azimuth; (c) following step (b), causing the percussion hammer to move the hammer bit alternately into and out of contact with the end of the well bore while simultaneously causing the motor to rotate the percussion hammer and the hammer bit about the central axes of the percussion hammer and the hammer bit thereby forming a new length of the well bore in the subterranean formation; and (d) concurrent with step (c), controlling the orientation of the bend in the motor housing in the well bore based on the one or more signals regarding the inclination and azimuth generated by the guidance system such that the new length of the well bore is within ±5°, inclusive, of horizontal in the subterranean formation.

A direction of movement of the hammer bit into and out of contact with the end of the well bore can be substantially parallel with the central axes of the percussion hammer and the hammer bit.

The new length of the well bore that is within ±5°, inclusive, of horizontal in the subterranean formation is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet.

Step (a) can include drilling the well bore utilizing a first drill bit. The method can further include, prior to step (b), removing the first drill bit from the well bore.

The bottom hole assembly can further include a drill pipe coupled between the guidance system and the surface. The weight of the drill pipe and the bottom hole assembly can urge the hammer bit toward the end of the well bore.

A rate of penetration of the hammer bit in the subterranean formation to form the new length of the well bore is desirably greater than 40 feet per hour, more desirably greater than 60 feet per hour, and most desirably greater than 80 feet per hour.

The bottom hole assembly can further include a shock assembly coupled between the guidance system and the motor assembly. The shock assembly is operative for mitigating vibration received by the guidance system caused by the operation of the hammer bit, the percussion hammer, and the motor.

Step (c) can include providing compressed fluid to the percussion hammer to cause the percussion hammer to move the one end of the hammer bit alternately into and out of contact with the end of the well bore. Also or alternatively, step (c) can include providing compressed fluid to the motor to cause the motor to rotate the percussion hammer and the hammer bit about the central axes of the percussion hammer and the hammer bit.

The angle of the bend in the motor housing can be between 0.2° and 1.5°.

Also disclosed herein is a method of drilling a subterranean formation that comprises: (a) positioning a drill string in a well bore in a subterranean formation, the drill string including: a hammer bit positioned at an end of the well bore, a bend in a housing of the drill string, and a guidance system operative for determining inclination and azimuth of at least a portion of the drill string in the well bore and for generating one or more signals regarding the inclination and azimuth; (b) following step (a), causing the hammer bit to repeatedly strike the end of the well bore while rotating the hammer bit about an axis of the hammer bit thereby drilling the subterranean formation and forming a new length of the well bore in the subterranean formation; and (c) controlling the orientation of the bend of the drill string in the well bore based on the one or more signals regarding the inclination and azimuth generated by the guidance system such that the hammer bit drills the new length of the well bore substantially horizontally in the subterranean formation.

The hammer bit desirably moves in a direction along its axis when the hammer bit is repeatedly striking the end of the well bore.

The new length of the well bore that is substantially horizontal in the subterranean formation is desirably between ±5°, inclusive, of horizontal in the subterranean formation.

The new length of the well bore that is within ±5°, inclusive, of horizontal in the subterranean formation is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet.

A rate of penetration of the hammer bit in the subterranean formation to form the new length of the well bore is desirably greater than 40 feet per hour, more desirably greater than 60 feet per hour, and most desirably greater than 80 feet per hour.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic view of a well bore that has been pre-drilled from a surface into a subterranean formation in which a bottom hole assembly is positioned; and

FIG. 2 is an isolated and exploded schematic view of the bottom hole assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with reference to the accompanying figures where like reference numbers correspond to like elements.

With reference to FIG. 1, a bottom hole assembly (BHA) 2 is shown at the bottom of a well bore 4 in a subterranean formation 6, which can be, for example, without limitation, a coal seam. Bottom hole assembly 2 is positioned at an end 8 of well bore 4 after formation of well bore 4 by way of another drill string (not shown) that utilizes a conventional drill bit such as, without limitation, a polycrystalline diamond compact (PDC) bit or a tri-cone bit. Once well bore 4 has been formed and the other drill string has been removed from well bore 4, bottom hole assembly 2 is positioned at end 8 of well bore 4 in subterranean formation 6.

As shown in FIG. 1, well bore 4 is an articulated well bore that includes a substantially vertical portion 10, a substantially horizontal portion 12, and a curved or radiused portion 14 interconnecting the vertical and horizontal portions 10 and 12. The horizontal portion 12 desirably lies substantially in subterranean formation 6.

A drill pipe 16 extends between a surface S through vertical portion 10, curved portion 14 and horizontal portion 12 of well bore 4 and connects to bottom hole assembly 2 positioned at end 8 of well bore 4. A pressurized fluid source, such as, without limitation, an air compressor 18, is coupled via a fluid line 20 to bottom hole assembly 2 in a manner to supply compressed fluid, such as, without limitation, compressed air, to one or more components or elements of bottom hole assembly 2 described hereinafter. The description herein of air compressor 18 supplying compressed air to one or more components of bottom hole assembly 2, however, is not to be construed as limiting the invention since it is envisioned that any other suitable and/or desirable means for supplying any other suitable and/or desirable pressurized fluid or fluid under pressure, such as drilling oil, mud, and the like, that is suitable and/or desirable for use as a source of fluid power for the one or more components of bottom hole assembly 2 is envisioned. Also or alternatively, it is envisioned that each component described hereinafter that utilizes pressurized fluid or fluid under pressure as a source of energy can be replaced with a comparable electrically powered device that performs the same function. For the purpose of simplicity in describing the present invention, the use of air compressor 18 supplying compressed/pressurized air to the one or more components of bottom hole assembly 2 via fluid line 20 will be described. However, for the reasons discussed above, this is not to be construed as limiting the invention.

Desirably, a computer 22 or other similar control means is connected via a communication cable 24 to a continuous guidance system 42 (shown in FIG. 2) of bottom hole assembly 2. Computer 22 is programmed to process data and/or signals regarding inclination and azimuth output by continuous guidance system 42 when bottom hole assembly 2 is positioned in well bore 4 and to output said inclination and azimuth data and/or signals in any suitable and/or desirable human readable form that facilitates the determination of the direction of at least a portion of bottom hole assembly 2 in well bore 4, and, hence, the direction of well bore 4. Also or alternatively, the data and/or signals regarding inclination and azimuth output by continuous guidance system 42 can be processed manually to determine the direction of at least a portion of bottom hole assembly 2 in well bore 4, and, hence, the direction of well bore 4. The combination of bottom hole assembly 2 and drill pipe 16 comprise a drill string 26.

With reference to FIG. 2 and with continuing reference to FIG. 1, in one non-limiting embodiment, bottom hole assembly 2 includes the following components or elements: a hammer bit 28, a percussion hammer 30, a positive displacement motor 32, a shock subassembly 34, a float subassembly 36, a three-point stabilizer 38, a universal bore hole orientation subassembly (UBHO) 40, which includes continuous guidance system 42 therein, and one or more non-magnetic drill collars 44.

The illustration in FIG. 2 and the discussion herein of bottom hole assembly having components 28-44 is not to be construed as limiting the invention since it is envisioned that bottom hole assembly 2 can include other components not shown but deemed necessary and/or desirable by one of ordinary skill in the art. For example, one skilled in the art may deem it necessary and/or desirable to include a crossover subassembly (not shown) between percussion hammer 30 and positive displacement motor 32 to facilitate the supply of pressurized air to percussion hammer 30 via positive displacement motor 32. Again, however, this is not to be construed as limiting the invention. Moreover, unless expressly set forth herein, the presence of each component shown in FIG. 2 and/or the arrangement of components shown in FIG. 2 is not to be construed as limiting the invention since the presence of any component and/or its position in the components comprising bottom hole assembly 2 shown in FIG. 2 may be determined by the application.

In use of bottom hole assembly 2, hammer bit 28 is positioned at end 8 of well bore 4 and the other end of bottom hole assembly 2, albeit UBHO subassembly 40 or one or more non-magnetic drill collars 44, is connected to drill pipe 16.

In the embodiment described herein, percussion hammer 30 utilizes compressed air to deliver high energy impulses to hammer bit 28 which, in turn, crushes the rock forming subterranean formation 6 with repeated blows. To this end, percussion hammer 30 is operative to forcibly cause hammer bit 28 to move alternately and repeatedly back-and-forth, to-and-fro, into and out of contact with end 8 of well bore 4 thereby crushing the rock forming subterranean formation 6. Percussion hammer 30 is based on the same technology used in construction jackhammers. The construction and use of percussion hammer 30 is well known in the art.

The end of hammer bit 28 utilized to repeatedly impact end 8 of well bore 4 includes an array of inserts 29, e.g., without limitation, diamond inserts, that project outward from the face of hammer bit 28 for impacting the rock forming subterranean formation 6. The compressed air utilized to operate percussion hammer 30 in a manner to cause hammer bit 28 to repeatedly impact end 8 of well bore 4 is exhausted from the face of hammer bit 28. The air exhausted from the face of hammer bit 28 can be utilized to remove crushed rock from end 8 of well bore 4 in a manner known in the art.

In operation of percussion hammer 30, compressed air from air compressor 18 builds up within percussion hammer 30 until an impact cylinder 46 of percussion hammer 30 is activated in a manner known in the art thereby causing inserts 29 of hammer bit 28 to forcibly move into contact with end 8 of well bore 4 thereby crushing and breaking the rock forming subterranean formation 6. The operation of hammer bit 28 and percussion hammer 30 are well known in the art and will not be described further herein for the purpose of simplicity.

In the embodiment described herein, positive displacement motor 32 includes an internal, compressed air driven motor 48 that has a fixed stator (not shown) and a rotor (not shown) that is operative for rotating within the fixed stator in response to compressed air being supplied to motor 48. In operation, motor 48 is coupled to percussion hammer 30 and is responsive to the supply of pressurized air from air compressor 18 for rotating percussion hammer 30 and hammer bit 28 substantially about central axes 50 and 52 of hammer bit 28 and percussion hammer 30, respectively. More specifically, compressed air supplied to motor 48 causes the rotor of motor 48 to rotate about a central axis 54 of motor 48 thereby rotating percussion hammer 30 and hammer bit 28 about central axes 50 and 52. Positive displacement motor 32 includes a housing 56 which supports the stator of motor 48 and which does not rotate when motor 48 rotates percussion hammer 30 and hammer bit 28 in response to compressed air being supplied to motor 48.

Housing 56 of positive displacement motor 32 includes a bend 58 therein that defines an angle θ between a first end 60 of positive displacement motor 32, which is desirably aligned with percussion hammer 30 and hammer bit 28, and a second end 62 of positive displacement motor 32 which is offset at angle θ with respect to first end 60. Desirably, angle θ of bend 58 is between 0.2% and 1.5%; however, the use of other angles is envisioned.

The description herein of positive displacement motor 32 and its operation is for the purpose of imparting a general understanding of the features and operation of positive displacement motor 32 and is not to be construed as limiting the invention. The operation of positive displacement motor 32 is well known in the art and will not be described further herein for the purpose of simplicity.

Bend 58 facilitates steering of bottom hole assembly 2 within well bore 4 for control of the direction that bottom hole assembly 2 drills subterranean formation 6. More specifically, the orientation of bend 58 in well bore 4 can be set by rotating the end of drill pipe 16 at surface S. In response to rotating the surface S end of drill pipe 16, bottom hole assembly 2 rotates about its longitudinal axis in well bore 8. By way of this rotation, the rotational orientation of bottom hole assembly 2 and, hence, bend 58 within well bore 4 can be adjusted.

Shock subassembly 34 is desirably disposed between positive displacement motor 32 and UBHO subassembly 40 for mitigating vibration received by UBHO subassembly 40 and, hence, continuous guidance system 42 due to the operation of hammer bit 28, percussion hammer 30, and motor 48 of positive displacement motor 32. To this end, compressed air supplied to percussion hammer 30 and positive displacement motor 32 from air compressor 18 causes percussion hammer 30 and positive displacement motor 32 to move violently. The striking of subterranean formation 6 by hammer bit 28 produces vibrations that could potentially have a negative effect on the internal components of continuous guidance system 42. Shock subassembly 34 mitigates these vibrations to permit bottom hole assembly 2 and, more particularly, continuous guidance system 42 to perform at a high level and protect continuous guidance system 42 from premature failure or damage.

Float subassembly 36 is operative for preventing well borne fluid from entering bottom hole assembly 2 and also ensures that the flow of compressed air to percussion hammer 30 and positive displacement motor 32 travels only in the direction toward percussion hammer 30 and positive displacement motor 32. To this end, float subassembly 36 acts in a manner of a one-way check valve restricting the flow of compressed air back toward air compressor 18.

Three-point stabilizer 38, or any other suitable and/or desirable stabilizer, can be utilized to center bottom hole assembly 2 in well bore 4. Three-point stabilizer 38 provides one or more points of contact with a wall section of well bore 4 that is a predetermined distance from the insert 29 end of hammer bit 28. This distance can be adjusted by adding one or more additional subassemblies between three-point stabilizers 38 and, for example, positive displacement motor 32. Also or alternatively, one or more additional three-point stabilizers 38 can be added to bottom hole assembly 2 as deemed suitable and/or desirable to control the build (rise) or drop (fall) tendencies of bottom hole assembly 2 during further drilling of well bore 4 with bottom hole assembly 2.

UBHO assembly 40 houses continuous guidance system 42. In one non-limiting embodiment, continuous guidance system 42 includes one or more accelerometers that provide inclination (up and down angle) data and/or signals, and one or more magnetometers that provide azimuth (left and right angle) data and/or signals that can be processed manually or automatically by computer 22. Continuous guidance system 42, including the accelerometers and the magnetometers thereof, is secured in place in UBHO subassembly 40. When bottom hole assembly 2 is assembled, continuous guidance system 42, including the accelerometers and the magnetometers thereof, are positioned a predetermined distance from the insert 29 end of hammer bit 28. Moreover, when bottom hole assembly 2 is assembled, the alignment between UBHO assembly 40 and, hence continuous guidance system 42, and the second end 62 of positive displacement motor 32 is fixed, whereupon the relation between the orientation of bend 58 and the data and/or signals output by the accelerometers and/or magnetometers of continuous guidance system 42 can be established. Hence, once bottom hole assembly 2 is positioned at end 8 of well bore 4 as shown in FIG. 1, the orientation of bend 58 in well bore 4 can be determined by the data and/or signals output by the accelerometers and/or the magnetometers of continuous guidance system 42.

For example, suppose it is desired that during drilling of a new section 64 in subterranean formation 6 with bottom hole assembly 2, that bottom hole assembly 2 build (rise) in said new section 64. To facilitate this build or rise, bottom hole assembly 2 is rotated about its longitudinal axis in well bore 4, whereupon the orientation of bend 58 in well bore 4 is also controlled, by rotating the surface S end of drill pipe 16 with reference to the data and/or signals output by the accelerometers and magnetometers of continuous guidance system 42 regarding the inclination and azimuth of continuous guidance system 42, until the inserts 29 end of hammer bit 28 is oriented in a direction that will cause bottom hole assembly 2 to build (rise) in subterranean formation 6 when drilling new section 64 of well bore 4 in subterranean formation 6. In one non-limiting example of such orientation of the inserts 29 end of hammer bit 28, second end 62 of positive displacement motor 32 can be positioned against the bottom of well bore 4 and the first end 60 of positive displacement motor 32 and, hence, percussion hammer 30 and hammer bit 28, can be positioned at angle θ (of bend 58) away from the bottom of well bore 4. Thus, by simply rotating the surface S end of drill pipe 16, the orientation of bend 58 in well bore 4 can be controlled based on the one or more data and/or signals regarding inclination and azimuth output by continuous guidance system 42, whereupon the distal end of hammer bit 28 can be aimed and steered as desired when forming new section 64 of well bore 4.

Lastly, the one or more non-magnetic drill collars 44 coupled to UBHO assembly 40 facilitate easier bending of the drill string 26 comprised of drill pipe 16 and bottom hole assembly 2 and avoids the presence of magnetic material adjacent UBHO subassembly 40 that may interfere with the operation of continuous guidance system 42.

Having thus described bottom hole assembly 2 and the environment in which bottom hole assembly 2 is utilized, the operation of bottom hole assembly 2 to form new length 64 of well bore 4 will now be described.

Initially, as described above, well bore 4 is formed from surface S into subterranean formation 6 utilizing a first drill string (not shown) having a first style drill bit, such as a PDC bit or a tri-cone bit. Desirably, the first drill string foams vertical portion 10, curved portion 14, and the first 75-100 feet of horizontal portion 4 of well bore 4. Once well bore 4 has initially been formed, the first drill string is extracted from well bore 4.

Next, drill string 26 comprising drill pipe 16 and bottom hole assembly 2 is positioned in well bore 4 with bottom hole assembly 2 positioned at end 8 of well bore 4 in subterranean formation 6 as shown in FIG. 1. In one non-limiting embodiment, bottom hole assembly 2 includes the following components in order between end 8 of well bore 4 and surface S: hammer bit 28, percussion hammer 30, a motor assembly, and continuous guidance system 42. In one non-limiting embodiment, the motor assembly comprises positive displacement motor 32 including motor 48 and housing 56 having bend 58 therein that defines an angle between first end 60 of positive displacement motor 32, which is aligned with percussion hammer 30 and hammer bit 28, and second end 62 of positive displacement motor 32. Bottom hole assembly 2 can also include one or more of the other components 34, 36, 38, and/or 44 as deemed necessary.

Once bottom hole assembly 2 is positioned at end 8 of well bore 4 with the central axis 50 of hammer bit 28 facing in a desirable direction in well bore 4, as determined by the data and/or signals output by continuous guidance system 42 given the fixed relationship between bend 58 and continuous guidance system 42, percussion hammer 30 is caused to move hammer bit back-and-forth, to-and-fro, into and out of contact with end 8 of well bore 4 while motor 48 of positive displacement motor 32 is caused to rotate percussion hammer 30 and hammer bit 28 about central axes 52 and 50, respectively, thereby forming new length or section 64 of well bore 4 in subterranean formation 6. During drilling of new length 64 of well bore 4, the weight of drill pipe 16 and bottom hole assembly 2 urges the inserts 29 end of hammer bit 28 toward end 8 of well bore 4.

The operation of percussion hammer 30 and motor 48 to form the new length 64 of well bore 4 described above is occasioned by supplying pressurized air from air compressor 18 to percussion hammer 30 and motor 48 via fluid line 20. Terminating the supply of pressurized air to percussion hammer 30 and motor 48 terminates their operation.

If desired, fluid controlled percussion hammer 30, fluid controlled motor 48, or both, can be replaced with any other suitable and/or desirable means, such as, without limitation, one or more electric motors that perform the same function. Accordingly, the description herein of operating percussion hammer 30 and hammer bit 28 by way of pressurized air is not to be construed as limiting the invention.

Concurrently with causing the operation of percussion hammer 30 and motor 48 in the manner described above, the orientation of bend 58 of housing 56 of positive displacement motor 32 in well bore 4 is controlled during the formation of new section 64 of well bore 4 based on the one or more data and/or signals regarding inclination and azimuth output by guidance system 42 such that new length 64 of well bore 4 is within ±5° degrees, inclusive, of a horizontal direction 66 (with respect to the force of gravity) in subterranean formation 6. As discussed above, the physical orientation of bend 58 in well bore 4 can be controlled by rotating the surface S end of drill pipe 16. It is envisioned that the orientation of bend 58 in well bore 4 can be controlled by: manually rotating drill pipe 16 based on the one or more data and/or signals output by guidance system 42; automatically rotating drill pipe 16 via a suitable means for rotating 68 coupled to drill pipe 16 and operating under the control of computer 22 which rotates drill pipe 16 based on the one or more data and/or signals output by guidance system 42; or some combination thereof.

It has been observed that the length of new section 64 of well bore 4 that is within ±5°, inclusive, of horizontal direction 66 in subterranean formation 6 is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet.

It has also been observed that percussion hammer 30 and motor 48 can be operated in a manner whereupon the rate of penetration of hammer bit 28 in subterranean formation 6 to form new length 64 of well bore 4 is desirably greater than 40 feet per hour, more desirably greater than 60 feet per hour, and most desirably greater than 80 feet per hour.

As discussed above, shock subassembly 34 disposed between guidance system 42 and positive displacement motor 32 is operative for mitigating vibration caused by the operation of hammer bit 28, percussion hammer 30, and motor 48 that is received by guidance system 42 during drilling of the new length 64 of well bore 4. Shock subassemblies, like shock subassembly 34, are known in the art and will not be described further herein for the purpose of simplicity.

In another simplified embodiment of drilling a subterranean formation, a drill string comprised of bottom hole assembly 2 and drill pipe 16 is positioned in well bore 4 in subterranean formation 6, with bottom hole assembly 2 positioned at end 8 of a well bore 4. This drill string includes hammer bit 28 positioned at end 8 of the well bore 4, a bend 58 in a housing 56 of the drill string, and a guidance system 42 operative for determining inclination and azimuth of at least a portion of the drill string in well bore 4 and for generating one or more data and/or signals regarding said inclination and azimuth. Once the drill string is positioned in well bore 4, hammer bit 28 is caused to repeatedly strike the end 8 of well bore 4 while hammer bit 28 is rotated about its axis 50 thereby drilling subterranean formation 6 and forming new length 64 of well bore 4 in subterranean formation 6. During the drilling of new length 64 of well bore 4, the orientation of bend 58 of the drill string in well bore 4 is controlled (either manually, automatically via means for rotating 68 operating under the control of computer 22, or both) based on the one or more signals regarding inclination and azimuth generated by guidance system 42, whereupon hammer bit 28 drills new length 64 of well bore 4 substantially horizontally (±5°, inclusive, of the horizontal direction 66) in subterranean formation 6. The orientation of bend 58 during the formation of the new length 64 of well bore 4 is desirably controlled by rotating drill pipe 16 of the drill string. However, independent rotation of bottom hole assembly 2 without rotating drill pipe 16 is also envisioned by way of a suitable means that can effect independent rotation of bottom hole assembly 2 with respect to non-rotation of drill pipe 16.

Desirably, hammer bit 28 moves back-and-forth in a direction along its axis 50 when hammer bit 28 is caused to repeatedly strike end 8 of well bore 4. The new length 64 of well bore 4 that is within ±5°, inclusive, of the horizontal direction 66 in subterranean formation 6 is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet. The rate of penetration of hammer bit 28 in subterranean formation 6 to form new length 64 of well bore 4 is desirably greater than 40 feet per hour, more desirably greater than 60 feet per hour, and most desirably greater than 80 feet per hour.

The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

1. A method of drilling a subterranean formation comprising: (a) forming a well bore from a surface into the subterranean formation; (b) positioning a bottom hole assembly at an end of the well bore in the subterranean formation, the bottom hole assembly including in order between the end of the well bore and the surface: a hammer bit; a percussion hammer operative for causing the hammer bit to move alternately into and out of contact with the end of the well bore; a motor assembly having a first end coupled to the percussion hammer, the motor assembly including a motor operative for rotating the percussion hammer and the hammer bit about central axes of the percussion hammer and the hammer bit, the motor assembly including a motor housing having a bend therein that defines an angle between the first end of the motor assembly and a second end of the motor assembly; and a guidance system operative for determining inclination and azimuth of at least a portion of the bottom hole assembly in the well bore and for generating one or more signals regarding the inclination and azimuth; (c) following step (b), causing the percussion hammer to move the hammer bit alternately into and out of contact with the end of the well bore while simultaneously causing the motor to rotate the percussion hammer and the hammer bit about the central axes of the percussion hammer and the hammer bit thereby forming a new length of the well bore in the subterranean formation; and (d) concurrent with step (c), controlling the orientation of the bend in the motor housing in the well bore based on the one or more signals regarding the inclination and azimuth generated by the guidance system such that the new length of the well bore is within ±5°, inclusive, of horizontal in the subterranean formation.
 2. The method of claim 1, wherein a direction of movement of the hammer bit into and out of contact with the end of the well bore is substantially parallel with the central axes of the percussion hammer and the hammer bit.
 3. The method of claim 1, wherein the new length of the well bore that is within ±5°, inclusive, of horizontal in the subterranean formation is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet.
 4. The method of claim 1, wherein: step (a) includes drilling the well bore utilizing a first drill bit; and the method further includes, prior to step (b), removing the first drill bit from the well bore.
 5. The method of claim 1, wherein: the bottom hole assembly further includes a drill pipe coupled between the guidance system and the surface; and the weight of the drill pipe and the bottom hole assembly urge the hammer bit toward the end of the well bore.
 6. The method of claim 1, wherein a rate of penetration of the hammer bit in the subterranean formation to form the new length of the well bore is desirably greater than 40 feet per hour, more desirably greater that than 60 feet per hour, and most desirably greater than 80 feet per hour.
 7. The method of claim 1, wherein the bottom hole assembly further includes a shock assembly coupled between the guidance system and the motor assembly, the shock assembly operative for mitigating vibration received by the guidance system caused by the operation of the hammer bit, the percussion hammer, and the motor.
 8. The method of claim 1, wherein step (c) includes providing compressed fluid to the percussion hammer to cause the percussion hammer to move the one end of the hammer bit alternately into and out of contact with the end of the well bore.
 9. The method of claim 1, wherein step (c) includes providing compressed fluid to the motor to cause the motor to rotate the percussion hammer and the hammer bit about the central axes of the percussion hammer and the hammer bit.
 10. The method of claim 1, wherein the angle is between 0.2° and 1.5°.
 11. A method of drilling a subterranean formation comprising: (a) positioning a drill string in a well bore in a subterranean formation, the drill string including: a hammer bit positioned at an end of the well bore, a bend in a housing of the drill string, and a guidance system operative for determining inclination and azimuth of at least a portion of the drill string in the well bore and for generating one or more signals regarding the inclination and azimuth; (b) following step (a), causing the hammer bit to repeatedly strike the end of the well bore while rotating the hammer bit about an axis of the hammer bit thereby drilling the subterranean formation and forming a new length of the well bore in the subterranean formation; and (c) controlling the orientation of the bend of the drill string in the well bore based on the one or more signals regarding the inclination and azimuth generated by the guidance system such that the hammer bit drills the new length of the well bore substantially horizontally in the subterranean formation.
 12. The method of claim 11, wherein the hammer bit moves in a direction along its axis when the hammer bit repeatedly strikes the end of the well bore.
 13. The method of claim 11, wherein the new length of the well bore that is substantially horizontal in the subterranean formation is between ±5°, inclusive, of horizontal in the subterranean formation.
 14. The method of claim 13, wherein the new length of the well bore that is within ±5°, inclusive, of horizontal in the subterranean formation is desirably longer than 500 feet, more desirably longer than 1,000 feet, and most desirably longer than 2,000 feet.
 15. The method of claim 11, wherein a rate of penetration of the hammer bit in the subterranean formation to form the new length of the well bore is desirably greater than 40 feet per hour, more desirably greater than 60 feet per hour, and most desirably greater than 80 feet per hour. 